The invention relates to new borosilicate glasses.
The technical literature discloses numerous borosilicate glasses having a high percentage of silicic acid (70-80%), a proportion of boric acid (7-13%), alkali-metal oxides (Na.sub.2 O, K.sub.2 O, 4-8%) and aluminium oxide (2-7%) and, if required, alkaline earth oxides (CaO, BaO, 0-5%). Characteristic features of these glasses are high chemical resistance (hydrolytic class 1, acid class 1), low thermal expansion and high temperature stressability.
For example, U.S. Pat. No. 4,386,164 describes a borosilicate glass of the following composition:
SiO.sub.2 : 70 to 74% by weight PA1 B.sub.2 O.sub.3 : 9 to 13% by weight PA1 Al.sub.2 O.sub.3 : 5 to 8% by weight PA1 Na.sub.2 O: 5 to 8% by weight PA1 K.sub.2 O: 0 to 4% by weight PA1 CaO: 0 to 3% by weight PA1 MgO: 0 to 1% by weight. PA1 Hydrolytic resistance according to DIN 12111: class 1. PA1 Acid resistance to DIN 12116: class 1. PA1 Caustic solution resistance to DIN 52322: class 2. PA1 Linear thermal expansion alpha (20.degree.-300.degree. C.): 4.3-5.0.times.10.sup.-6 K.sup.-1 PA1 Resistance to thermal shocks: .gtoreq.110 K. PA1 X-ray absorption .mu. at 0.6 .ANG.: .ltoreq.5.3 cm.sup.-1 PA1 Transformation temperature Tg: 535.degree. to 570.degree. C. PA1 Processing temperature V.sub.A : 1140.degree. to 1220.degree. C. PA1 SiO.sub.2 : 74.5 to 76.5% by weight PA1 B.sub.2 O.sub.3 : 10.0 to 12.0% by weight PA1 Al.sub.2 O.sub.3 : 3.5 to 6.0% by weight PA1 Na.sub.2 O: 6.0 to 8.0% by weight PA1 CaO: 1.0 to 2.0% by weight PA1 ZrO.sub.2 : 0 to 0.50% by weight PA1 F: 0 to 1.0% by weight PA1 SiO.sub.2 75.25% by weight PA1 B.sub.2 O.sub.3 : 11.00% by weight PA1 Al.sub.2 O.sub.3 : 5.10% by weight PA1 Na.sub.2 O: 7.00% by weight PA1 CaO: 1.40% by weight PA1 F: 0.25% by weight
This glass has the required good chemical and temperature-resistance for use in the laboratory, but it is not suitable for other purposes, for example as domestic glass, lamp glass or X-ray tube glass.